The purpose of this project is to define the immunochemical characteristics of selected components that are exposed on the exteriors of gonococci. This information is intended to provide background data on which design of vaccines to prevent gonorrhea can be based. During the past year, the project has concentrated on study of two groups of outer membrane proteins--protein III and protein II. The protein III constituents were found to be constant in presence and immunochemical reactivity among all strains and substrain variants of gonococci. The protein III moieties are surface-exposed and are potential targets for bactericidal actions of antibodies. Proteins of identical immunochemical reactivities as gonococcal protein III but different (from gonococci) subunit sizes were found on several other neisseriae including both meningococci and commensual species. Outer membrane protein II moieties were found to be highly variable both in occurrence and immunochemical characteristics on variants of individual strain and among diverse strains. All protein II forms exhibit common antigenicities, but these common regions appear buried on the organisms' outer membranes; exposed portions of protein II appear to be unique, in general, though some examples of cross-reactivities were found both within a given strain and among different strains. More than one protein II can coexist on individual gonococci.